Adjustable potentiometer



Nov. 10, 1964 BLANCO 3,156,888

ADJUSTABLE POTENTIOMETER Filed March 1, 1963 .2 Sheets-Sheet 1 40b INVENTOR. 22 2/ ELIAS BLA/VCO Nov. .10, 1964 E. BLANCO ADJUSTABLE POTENTIOMETER 2 Sheets-Sheet 2 Filed Mamh l, 1965 INVENTOR EL I145 BLANCO United States Patent 3,156,888 ADJUSTABLE POTENTIOMETER Elias Blanca, Los Angeles, Calif., assignor to Weston Instruments, Inc., a corporation of Texas Filed Mar. 1, 1963, Ser. No. 262,006 1 Claim. (Cl. 338-149) This invention relates to adjustable potentiometers of the type having a helically-shaped resistance element and has for an object the provision of a slidable contact assembly for the potentiometer having stop settings at which the stopping forces are not applied to the assembly.

Potentiometers of the helically-shaped resistance element type are known by those skilled in the art to have a slidable contact assembly which moves axially of the potentiometer casing upon rotation of the shaft. These potentiometers are limited in their applications when a high torque is applied in turning the shaft and particularly, at the stop settings. With high torque at the stop settings, a great amount of force is applied between the periphery and the center of the slidable contact assembly which causes it to cant or to tilt within the casing thus to produce instability as well as unbalance at the stop settings.

Accordingly, an object of the present invention is to provide an adjustable potentiometer which is maintained stable and in balance at the stop settings though a high torque be applied to the potentiometer shaft.

A further object of the invention is to provide a potentiometer in which the application of the stopping forces from the potentiometer shaft to the casing is accomplished through novel structure rather than through the slidable assembly.

In accordance with the present invention there is disposed longitudinaliy of the potentiometer shaft an elongated guide member adapted to rotate about the axis of the shaft. The slidable contact assembly includes first stop means which slidably engages the guide member, and upon rotation of the shaft, the assembly and the first stop means move axially of the casing with the contact slidably engaging the resistance element. In co-operative relationship with the first stop means there is provided second stop means which, upon engagement with the first stop means, halts the contact assembly. In this manner, the stopping forces are transmitted from the shaft, through the guide member, the first and second stop means and to the casing, and thus the stopping forces are not applied to and thus avoid the movable contact assembly.

More particularly, in carrying out the present invention in one form thereof, flanges are secured to the rotatable shaft and disposed adjacent the respective ends of the resistance element. At least two guide members are disposed parallel to the shaft and between the flanges with their respective ends being secured to the flanges. A sleeve stop slidably engages one of the guide members having its outer periphery secured to the slidable contact assembly which slidably engages the other one of the guide members. The sleeve stop protrudes from each face of the assembly and co-operates with fixed stops, each secured to the casing and adjacent to the respective ends of the resistance element, defining the limits of travel of the assembly. Accordingly, when one end of the sleeve stop engages a fixed stop, the stopping forces are applied by way of the shaft through the flanges, the guide member carrying the sleeve, the sleeve'stop, throughthe fixed stop and then to the casing. Accordingly, the stopping forces are not applied to the assembly but rather to novel structure constructed and arranged to provide a high torque rating for the potentiometer. In this manner, the potentiometer is in balance and is stable at all settings, and particularly, at the stop settings.

For further objects and advantages of the invention, and for a description of its operation, reference is to be had to the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an adjustable potentiometer embodying the present invention;

FIG. 2 is a perspective exploded view of the potentiometer of FIG. 1;

FIG. 3 is a side cross-sectional view of the potentiometer of FIG. 1 taken along the line 3-3 in FIG. 4;

FIG. 4 is a front cross-sectional view of the potentiometer of FIG. 1 taken along the line 44 in FIG. 3; and,

FIGS. 5 and 6 are perspective views of the potentiometer of FIG. 1 with portions of the structure in phantom to show the operation of the potentiometer in both extremes of contact travel.

Referring now to FIGS. 1-4, the potentiometer has been illustrated as including a housing or casing 10 made of electrically insulating material having a substantially cylindrical inner chamber 11 closed at both ends by end members 13 and 14. The end member 13 is of sufficient outer diameter to be snugly received within one end of the chamber 11. The end member 14 has an annular collar adapted to fit within the other end of chamber 11 and is secured to the casing 10 by fastening screws 16 which extend through openings in the end member 14 and into mating screw threaded openings in ears 17 of the casing 10.

A helical groove 21 is formed in the wall of the chamber 11 having disposed therein a resistance element 22. The resistance element 22 may comprise, for example, wound resistance wire of substantially small di ameter having its adjacent turns spaced from each other. The resistance wire is wound about an electrically insulated larger diameter wire that is disposed as a helix within the groove 21. Adjacent to each end of the resistance element 22 there are located conductive clips 25 received in openings in the casing 10 and within the protuberance 10a of the casing. The clips 25 are in electrical contact with the resistance wire and are each electrically connected to a respective exterior terminal 1% mounted on the protuberance 10a.

The end members 13 and 14 journal a control shaft or drive means 20 which extends through the end member 14 and the chamber 11 to the end memeber 13 and is positioned so that its center of rotation coincides with the axis of the helix formed by the resistance element 22. The shaft 20 is rotatably supported within an outwardly extending boss 14a of the end member 14 and is secured against movement in the longitudinal direction by a lock washer 14d. The boss 14a has an exterior thread for threadedly receiving mounting nut 14b and for receiving a Washer 140 for mounting the potentiometer to a panel. The other end of the shaft 20 is journalled in a central bore of the end member 13.

Square-shaped flanges 27 and 28 are disposed within the chamber 11 each located between a respective end member 13 and 14 and a respective end of the resistance element 22. Each of the fianges 27 and 28 is fixedly secured to the shaft by way of pins 30 so that the flanges rotate with the shaft and within the chamber 11. Guide or stop members 32 and 33 of rod-like shape are disposed parallel to the shaft 20 and between the flanges 27 and 28. The members 32 and 33 are secured to the flanges 27 and 28 at opposite corners thereof with the respective ends of the members being received within openings in the flanges and secured thereto by force fitting or by lock washers. Accordingly, upon rotation of the shaft 20, the members or rods32 and 33 are driven to rotate about the axis of the shaft 20.

A collector wire 35 of conductive material is also disposed parallel to the shaft 20 and between the flanges 27 and 28. The wire or bar 35 is received by an insulated member 36 seated in an opening in one of the remaining corners of the flange 28 and by an insulated member 38 seated in an opening in a corresponding corner of the flange 27. The wire 35 is electrically connected to a spring metal contact or wiper 35a secured to the insulated member 38 and in wiping contact with a conductive ring 46 secured to the housing and having a leg 47 electrically connected to an exterior terminal 48 mounted on the protuberance a.

A slidable contact assembly 49 is adapted to be supported by driven members 32 and 33 and is formed in the shape of a disc having a central opening of substantially rectangular shape to allow free passage of the shaft 20. In addition, the assembly 40 has openings for the members 32 and 33 and for the wire 35. A cylindrically shaped member a is secured to the assembly 43 for a supporting contact structure 43 which comprises a wiper 430 which contacts the resistance element 22 and a lower split stem 43b bifurcated to form a pair of fingers,

one of which bears against each side of the collector wire 35.

As well understood by those skilled in the art, the type and structure of the housing 10, the con-tact structure 43, the wire 35, and the like may vary depending upon specific applications and may be of the type as shown, for example, in US. Patent No. 2,900,614.

A sleeve stop 44 has a cylindrical inner chamber for slidably receiving the rod 32 and an annular exterior channel intermediate its ends for snugly receiving the assembly 40. The sleeve 44 protrudes from each face of the assembly 40 defining two washer shaped stops. The other rod 33 is slidably engaged by the opening in the assembly or carriage 40 and thus the assembly is adapted to move axially of the shaft 20 and of the casing 10 while slidably engaging the rods 32 and 33. In this manner, the assembly is supported by the rods with the assembly being rotated as the rods 32 and 33 are rotated about the central axis of the shaft.

The outer periphery of the assembly 40 adjacent the rods 32 and 33 is formed to define helical threads 46b for engaging the helical groove cut in the chamber 11. Accordingly, upon rotation of the shaft 20 the assembly 40 rotates about its central axis and also moves in a longitudinal direction axially of the shaft. As a result of the rotary and longitudinal movement of the assembly 40 with rotation of the shaft 20, the contact structure 43 travels in a helical path with the wiper 43c contacting the resistance element 22 and the fingers bearing against the wire 35. In this manner, as the shaft 20 is rotated, the wiper 43c contacts the entire length of the resistance element 22.

The electrical circuit from the wiper 43c may be traced from the contact structure 43 by way of the wire 35, wiper 35a, conductive ring 46 and leg 47, and to exterior terminal 48 mounted on the protuberance 10a. Mention has already been made that the exterior terminals 19b are connected to the resistance element 22 contacted by the wiper which completes the tracing of the electrical 'circuit for the potentiometer.

Fixed washer-shaped stops 5t) and .51 each have a plurality of outer ears Stia and 51a respectively, which are received in mating slots in the housing 10 for fixedly securing the stops 5t) and 51 to the housing. Ears 50b and 51b extend inwardly from the stops 50 and 51 respectively, with each of the ears providing a shoulder surface which is disposed in co-operative relationship with the movable sleeve stop 44. Accordingly, as best illustrated in FIGS. 5 and 6, the inner ears 5% and 5112 are positioned so that at each extreme of travel of the assembly 40, a mating surface or portion of the periphery of the sleeve stop 44 engages the shoulder of its respective inner car. More particularly, in operation of the potentiometer in the direction illustrated in FIG. 6, a portion of the periphery of the left hand end of the sleeve stop 44 engages a shoulder 510 of the inner ear 51b. It is to be noted that the entire width of the shoulder 51c is covered by the mating or co-operating portion of the periphery of the stop 44 to assure good mechanical contact between the elements. In this manner, the force applied from the sleeve stop 44 to the stop 51 is in a direction to tend to rotate the stop 51 in a clock-wise direction, but that stop is fixedly secured to the casing which is mounted on a fixed support such as a panel.

It will now be understood that the torque applied by rotation of the shaft 263 in the direction illustrated in FIG. 6 is transmitted from the shaft as a force through the pins 36, the flanges 27 and 28, through the rod stop 32, the sleeve stop 44, the inner ear 51b of the fixed stop 51, to the outer ears 51a thereof and then to the casing 10. Thus, in accordance with the present invention, the stopping forces totally avoid the assembly 4! and are taken up by structure which is constructed of material and designed of suflicient cross-section to withstand the above relatively large forces. In this manner, the assembly is maintained stable and in balance at the stop setting.

Referring now to FIG. 5, in operation of the potentiometer in the illustrated direction, a portion of the periphery of the right hand end of the sleeve stop 44 engages the shoulder 500 of the inner ear Stib in a manner similar to that described above with relation to the stop 51. The stop 44 tends to turn the stop 50 in a counterclockwise direction, but that stop is fixedly connected to the housing 10. Accordingly, the stopping forces are taken up by the shaft 20, the pins 30, the flanges 27 and 28, the rod stop 32, the sleeve stop 44, the fixed stop 50 and the housing 10.

Now that the principles of the invention have been explained, it will be understood that many modifications may be made. For example, instead of the two rods 32 and 33 illustrated in FIG. 2, there may be only a single rail or track member (not shown) being slidably engaged by a sleeve stop having secured thereto the contact assembly. In this manner, the assembly will be supported by and rotate with the single track member.

What is claimed is: V

A potentiometer comprising a housing,

an electrical resistance element supported in said housa shaft journalled for rotation in said housing,

two rods disposed in spaced parallel relation to and on opposite sides of said shaft,

means securing said rods to said shaft for rotation there with,

first stop means including a sleeve member slidably engaging one of said rods,

an assembly secured to said sleeve member intermediate the ends thereof and slidably engaging the other of said rods, adapted to be rotated with said shaft and rods,

means formed in said housing and on the periphery of said assembly for moving said assembly axially of said housing when said asembly is rotated,

References Cited in the file of this patent UNITED STATES PATENTS Beckman Nov. 30, 1948 Beckman June 14, 1949 Sorber Nov. 19, 1957 Miller Nov. 4, 1958 Marason May 19, 1959 Gach et a1. Aug. 18, 1959 Mucher Apr. 3, 1962 

